Fires related to unattended gas burners on a cooking surface have long been recognized as a problem in need of a practical, effective solution. In a 2001 report to the U.S. Consumer Product Safety Commission (the “Report”), Arthur D. Little reported on possible technologies that could address cooktop fires. The Report reviewed 111 technologies, most of which focused on systems designed to determine whether a person was in proximity of the range, systems to measure the temperature of a cooking utensil or a cooking surface, and systems to detect, warn, and extinguish a fire.
In the interval since 2001, it appears that no technology identified in the Report has been widely accepted as a means to address the hazard of home cooking fires. According to the National Fire Protection Association Fire Analysis and Research Division (the “NFPA”), between 2006 and 2010, fire departments in the United States responded to an average of 90,400 home structure fires per year in which a range or cooktop was involved as a contributing cause of the fire. Such fires caused an annual average of 330 civilian deaths, 3,740 reported civilian injuries, and $571 million in property damage. The NFPA also reported that between 2005 and 2009, 84% of civilian deaths which involved cooking equipment were due to fires involving cooking range tops.
Civanelli, U.S. Pat. No. 5,136,277, envisioned using charged capacitor plates on the cooking surface to sense when a cooking utensil, such as a pot or pan, was moved about the cooking surface. Shuler, U.S. Pat. No. 6,253,761, describes a weight sensor under a burner which communicates with a solenoid that turns a gas supply on when weight is detected and which turns the gas supply off when weight is removed from the burner. Higley, U.S. Pat. No. 5,628,242, describes a system that shuts off the gas supply to a gas grill that has not been used for a preselected time period. According to Higley, an adjustable timer is used to shut off the gas supply after no motion has been detected for a preselected time period. Motion detection is accomplished using a lid position sensor to detect when the grill lid is moved between the open and the closed position, a detector which monitors switch usage to detect activity, and a vibration or movement detector which monitors when the grill itself has been moved. Coppola, WO2008031645, describes the use of fiber optic sensors to sense when a pot or pan is on a cooking surface. If the pot or pan is detected, then gas is allowed to flow to the burner. A timer allows gas flow to the burner for a pre-set period of time after a pot or pan is no longer detected on the burner. Other devices are known which sense general movement around a range and then turn off the range if no movement is detected after a predetermined interval. The simplest prior art safety device is a timer which turns off the gas supply to a range if the range has been in use for twelve hours.
Each of the prior art devices only senses when a cooking utensil is on a burner surface when there is general motion in the vicinity of a range or when the range has been in use for too long a period of time. Depending on what type of meal is being prepared, weight sensors or fiber-optic sensors that are used to determine when a utensil is on a burner may not be practical. If a meal requires the regular removal and replacement of a utensil, such as when cooking with a wok, it may be difficult to find a timer setting that adequately covers the range of movements which accompany such cooking and the burner may be turned off prematurely or be left on long after cooking has ceased. Likewise, detectors which rely on movement of a cooking appliance itself or on sensing movement in the general vicinity of the range may prove impractical as events that are within the normal range of cooking activities may cause a gas burner to be shut down prematurely. Likewise, events that are not part of the cooking activities may cause a burner to stay lit when it should be shut down for safety reasons. Thus, such devices fail to operate in a way that is consistent with how a human operator uses a range.
Thus, one of the challenges the prior art devices fail to accommodate is the nearly infinite variations in size and shape of cooking utensils, as well as the size, shape and mannerisms of a human operator.
Other types of temperature sensors such as passive infrared sensors (“PIR sensors”) for example, do not actually detect the movement of an object or its presence; rather PIR sensors are electronic sensors which measure infrared radiation (“IR”) from objects within their field of view. All objects with a temperature above absolute zero emit heat energy in the form of IR which enables PIR sensors to detect changes in temperature at a given point. Such may be interpreted as the movement of an object. An item of constant temperature that does not move is invisible. A motionless item which changes temperature is visible. This poses a gap in detection which is problematic in the instance of a cooking utensil, such as a pot of tepid water, that is intentionally left to boil. Under constant boiling, the temperature of the pot may change so little that a PIR sensor may lack the sensitivity to detect such a change. A stationary utensil that is being tended to by a human operator who creates a separate heat signature and is moving in and out of the zone of detection of the PIR sensor may be difficult to monitor. Such difficulties in using PIR sensors and the like could lead to misreadings and inadvertent shut-offs of a gas burner.
Therefore, what is needed is a safety burner system which operates in an ergonomic fashion and which accommodates the range of activities likely to be performed around a burner while a meal is being prepared. What is further needed is a safety burner system that intelligently interacts with a human operator of a gas range.